If you are never going to drive it in the snow again why undercoat it? Paint will hold up just fine.If you undercoat it I would try the Rust Oleum brand.
Traditional (tar based?) undercoat adds considerable weight, and can come separated, leaving cracks and voids that gather dirt and moisture Mine is doing that is some places, and right at the moment I'm tearing the car down for paint. I'll hit the bottom with a pressure washer to knock some more of it off
Hell I barely drive mine in the rain, much less snow.
